Solitary magnocellular neurons in the homozygous Brattleboro rat have vasopressin and glycopeptide immunoreactivity

The bovine anterior hypothalamus: Characterization of the vasopressin-oxytocin containing nucleus and changes in relation to sexual differentiation

In an effort to systematically describe the neurochemical anatomy of the bovine anterior hypothalamus, we used a series of immunocytochemical markers such as acetylcholine esterase (AChE), arginine-vasopressin (AVP), calbindin (Calb), galanin (Gal), neuropeptide-Y (NPY), oxytocin (OXT), somatostatin (SST), and vasoactive intestinal peptide (VIP). We also investigated the potential sex difference present in the suprachiasmatic nucleus (SCN) and the vasopressin-oxytocin containing nucleus (VON) of six male and six female Bos taurus. Our study revealed that the cytochemical structure of the cattle anterior hypothalamus follows the blueprint of other mammals. The VON, which was never described before in cattle, showed a sex difference with a 33.7% smaller volume and 23.2% fewer magnocellular neurons (approximately 20-30 μm) in the male. The SCN also did show a sex difference in VIP neurons and volume with a 36.1% larger female nucleus with 28.1% more cells. Additionally, we included five heifers with freemartin syndrome as a new animal model relevant to sexual differentiation in the brain. This is, to the best of our knowledge, the first freemartin study in relation to the brain. Surprisingly, the SCN of freemartin heifers was 32.5% larger than its control male and female counterparts with 29% more VIP cells. Conversely, the freemartin VON had an intermediary size between male and female. To analyze our data, a classical statistical analysis and a novel multivariate and multi-aspect approach were applied. These findings shed new light on sexual dimorphism in the bovine brain and present this species with freemartins as a valuable animal model in neuroscience.

Somatic mutations in neurons during aging and neurodegeneration

The nervous system is composed of a large variety of neurons with a diverse array of morphological and functional properties. This heterogeneity is essential for the construction and maintenance of a distinct set of neural networks with unique characteristics. Accumulating evidence now indicates that neurons do not only differ at a functional level, but also at the genomic level. These genomic discrepancies seem to be the result of somatic mutations that emerge in nervous tissue during development and aging. Ultimately, these mutations bring about a genetically heterogeneous population of neurons, a phenomenon that is commonly referred to as "somatic brain mosaicism". Improved understanding of the development and consequences of somatic brain mosaicism is crucial to understand the impact of somatic mutations on neuronal function in human aging and disease. Here, we highlight a number of topics related to somatic brain mosaicism, including some early experimental evidence for somatic mutations in post-mitotic neurons of the hypothalamo-neurohypophyseal system. We propose that age-related somatic mutations are particularly interesting, because aging is a major risk factor for a variety of neuronal diseases, including Alzheimer's disease. We highlight potential links between somatic mutations and the development of these diseases and argue that recent advances in single-cell genomics and in vivo physiology have now finally made it possible to dissect the origins and consequences of neuronal mutations in unprecedented detail.

60 YEARS OF NEUROENDOCRINOLOGY: MEMOIR: Geoffrey Harris and my brush with his unit

Geoffrey Harris is chiefly known for his demonstration of the control of the pituitary gland by the portal vessels coming from the hypothalamus. This does not do justice to his extraordinary contribution to biology. Harris' life's work was central in demonstrating the brain/body interactions by which animals and humans adapt to their environment, and above all the control of that most crucial and proximate of all evolutionary events - reproduction. In this brief review, I have tried to put Geoffrey Harris' work in the context of the scientific thinking at the time when he began his work, and above all, the contribution of his mentor, FHA Marshall, on whose towering shoulders Harris rose. But this is mainly my personal story, in which I have tried to show the debt that my work owed to Harris and especially to my dear friend, the late Keith Brown-Grant in Harris' team. I myself was never an endocrinologist, but over a short period in the early 1970s, under the influence of such inspirational mentors, and using purely anatomical methods, I was able to demonstrate sexual dimorphism and hormone-dependent sexual differentiation in the connections of the preoptic area, regeneration of the median eminence, the ultrastructure of apoptosis, the requirement for the suprachiasmatic nuclei in reproductive rhythms, the existence of non-rod or cone photoreceptors in the albino rat retina and, later, the expression of vasopressin by solitary (one in 600) magnocellular neurons in the polydipsic di/di Brattleboro mutant rat; this phenomenon was subsequently shown to be due to a+1 reading frameshift. I end this brief overview by mentioning some of the abiding and fascinating mysteries of the endocrine memory of the brain that arise from Harris' work on the control of the endocrines, and by pointing out how the current interest in chronobiology emphasises what a Cinderella the endocrine mechanisms have become in current brain imaging studies.

The molecular neurobiology of stress--evidence from genetic and epigenetic models

Knowledge of the genetic and molecular events underlying the neuroendocrine and behavioural sequelae of the response to stress has advanced rapidly over recent years. The response of an individual to a stressful experience is a polygenic trait, but also involves non-genetic sources of variance. Using a combination of top-down (quantitative trait locus [QTL] and microarray analysis) and bottom-up (gene targeting, transgenesis, antisense technology and random mutagenesis) strategies, we are beginning to dissect the molecular players in the mediation of the stress response. Given the wealth of the data obtained from mouse mutants, this review will primarily focus on the contributions made by transgenesis and knockout studies, but the relative contribution of QTL studies and microarray studies will also be briefly addressed. From these studies it is evident that several neuroendocrine and behavioural alterations induced by stress can be modelled in mouse mutants with alterations in hypothalamic-pituitary-adrenal axis activity or other, extrahypothalamic, neurotransmitter systems known to be involved in the stress response. The relative contribution of these models to understanding the stress response and their limitations will be discussed.

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

Processing of frameshifted vasopressin precursors

Biosynthesis of the vasopressin (VP) prohormone in magnocellular neurones of the hypothalamo-neurohypophysial system comprises endoplasmic reticulum (ER) transit, sorting into the regulated secretory pathway and subsequent processing in the individual proteins VP, neurophysin and a glycoprotein. These processes are severely disrupted in the homozygous diabetes insipidus (di/di) Brattleboro rat, which expresses a mutant VP precursor due to a single nucleotide deletion in the neurophysin region of the VP gene resulting in VP deficiency. Previous studies have shown the presence of additional frameshift mutations in VP transcripts, in solitary magnocellular neurones of the di/di rat due to a GA dinucleotide deletion resulting in two different mutant VP precursors with partly restored reading frame. Frameshifted VP precursors are also expressed in several magnocellular neurones in wild-type rats. In this study, we determined if the +1 frameshifted precursors from di/di and wild-type rats can lead to biosynthesis of the hormone VP. Therefore, eukaryotic expression plasmids containing the frameshifted VP cDNAs were transiently expressed in peptidergic tumour cell lines, and cells were analysed by reversed phase high-performance liquid chromatography and specific radioimmunoassays, and by immunofluoresence. Neuro2A neuroblastoma cells expressing the +1 frameshifted precursors of di/di rats retained products in the cell body. Only precursor or insignificant quantities of neurophysin-immunoreactive products were detected. In contrast, in AtT20 cells, frameshifted VP precursors were at least partly processed to yield the VP peptide, indicating that they have access to the regulated secretory pathway. Comparison between the two cell lines showed a very slow ER transit of the wild-type prohormone combined with inefficient processing in Neuro2A cells. The results show that mutant precursors can reach the regulated secretory pathway if ER transport is sufficiently rapid as in the case of AtT20 cells. This suggests that the di/di rat may regain the capacity to biosynthesize authentic VP through these +1 frameshifted precursors in magnocellular neurones.

Genetic models of vasopressin deficiency

Animal models of genetic hormone deficiency are useful as models for physiological studies of hormone deficiency and hormone action. Structure-function studies of the specific underlying gene defect may help in understanding mechanisms regulating gene expression and secretion of the peptide product. Spontaneous genetic models of vasopressin deficiency, such as the Brattleboro rat and human familial diabetes insipidus, have facilitated many studies of vasopressin. However, the Brattleboro rat may not be an ideal model of genetic vasopressin deficiency and therefore could be less useful for studies of the central nervous system or as a background strain for the introduction of new vasopressin gene constructs. The human model is appropriately limited by the constraints of human studies, so that engineered animal models of specific diseases, such as familial neurohypophysial diabetes insipidus, are required. The recent development of a vasopressin-null mouse may provide insights into the various roles of vasopressin in the stress response, cardiovascular regulation and behaviour. Additionally, animals with a complete genetic deficiency of vasopressin can serve as a background strain for introduction of novel vasopressin gene constructs to enable sophisticated studies of the regulation of vasopressin expression and the intracellular processes required for appropriate secretion of vasopressin peptide. As advanced techniques of genetic manipulation become more reliable, conditional expression of vasopressin, regulated by time or body site will permit even more detailed studies in this field.

The magnocellular neurons of the hypothalamo-neurohypophyseal system display remarkable neuropeptidergic phenotypes leading to novel insights in neuronal cell biology

For decades the magnocellular neurons of the hypothalamo-neurophypophyseal system (HNS), in which either vasopressin or oxytocin are produced and released into the bloodstream, have been playing a pivotal role in fundamental discoveries in the nervous system. The primary structure of vasopressin and oxytocin was the first of all neuropeptides to be published, i.e., in the 1950s by the Nobel prize laureate Du Vigneaud. Moreover, many trend-setting discoveries have their origin in the HNS, which abundantly expresses vasopressin and oxytocin, clearly displays its function and is relatively easily to manipulate. Examples are the phenomenon of coexpression of neuropeptides, patch-clamping of nerve endings, axonal transport of RNA, neuroglia interactions and the behavioral effects. An extraordinarily intriguing example is the homozygous Brattleboro rat, which lacks vasopressin by a germ-line mutation, and has disclosed many of the fundamental characteristics of peptidergic neurons, and neurons in general. In this chapter we will discuss a few of them, in particular the recent data on mutations in vasopressin RNA. It is to be expected that the HNS will retain its informative role in the next decades.

Functions of the perikaryon and dendrites in magnocellular vasopressin-secreting neurons: new insights from ultrastructural studies

Magnocellular hypothalamic neurosecretory neurons secreting vasopressin or oxytocin provide a robust model system for the investigation and understanding of many aspects of peptidergic neuronal function. Many of their functions and the cellular organelles involved are well understood. However, recent ultrastructural studies have thrown new light on various aspects of magnocellular neurosecretory function which have not previously received much attention. This review concerns two of these: the effects of mutations in the vasopressin gene on the handling of the translated peptide by the rough endoplasmic reticulum; and the role of the magnocellular dendrites in the production, secretion and localisation of peptides. Investigation of the synthesis of proteins derived from vasopressin genes which have undergone various mutations has at the moment provided more answers than questions: Why do some abnormal products accumulate as masses of peptide in the rough endoplasmic reticulum while others do not? Why do accumulations in humans appear to be damaging to the neurons while those in the rat do not? Investigations of the role of dendrites in the production and release of peptides show that the dendrites have all the machinery needed for protein translation and appear to synthesize locally proteins required for dendritic function. Of particular interest is the possibility that various transmitter receptor proteins could be synthesized in the dendrites close to the synapses in which they become localized. Precisely how such membrane proteins are inserted into the synaptic complex is, however, unclear, because the most part of the dendrites lack any form of the Golgi packaging organelle that can be recognised as such either by immunocytochemistry or electron microscopy. Better established is the ability of magnocellular dendrites to secrete either vasopressin or oxytocin in response to a variety of stimuli including sex steroids. This local release of peptide into the magnocellular nuclei has important but as yet incompletely defined effects on the functioning of the neurons.

Immunocytochemical evidence for the presence of vasopressin in intermediate sized neurosecretory granules of solitary neurohypophyseal terminals in the homozygous Brattleboro rat

A single base deletion (delta G) in the vasopressin gene is the cause of diabetes insipidus in the homozygous Brattleboro rat (di/di). The resulting frameshift leads to the expression of an aberrant vasopressin precursor which is unable to enter the secretory pathway, thereby preventing vasopressin biosynthesis. In a small number of solitary magnocellular hypothalamic neurons within the supraoptic and paraventricular nuclei, the reading frame is restored by a dinucleotide (delta GA) frameshift mutation, at two separate GAGAG motifs downstream of the original G-deletion. This results in two + 1 di-vasopressin precursors that are still partially mutated within the neurophysin region. The present study provides immunocytochemical evidence which demonstrates that, within magnocellular solitary neurons of the supraoptic and paraventricular nuclei of the di/di rat, the + 1 di-vasopressin precursors can enter the secretory pathway followed by their enzymatic processing into vasopressin during axonal transport to the neural lobe. However, the cellular characteristics of biosynthesis are different from those of wild-type rats. Immunoelectron microscopical localization of vasopressin gene products in the neural lobe of did/di rats revealed their presence in neurosecretory granules, the diameter of which is intermediate (116 nm) between those of the neurosecretory granules in the di/di (80-100 nm) and wild-type (160 nm) rats.

Somatic mutations in the brain: relationship to aging?

Genetic instability is generally thought to underlie the process of aging and is predominantly associated with meiosis and mitosis. This review will discuss DNA damage and repair, somatic mutations and somatic recombination events in non-dividing neurons in relation to aging. In general it can be concluded that mutagenesis operates at high frequency in the brain. Present data do not provide clear evidence for accumulating DNA damage or a change in DNA repair activity in the brain with age. However, a linear age-related increase in frameshift mutations has been shown to occur in vasopressin neurons of the rat, revealing a novel post-mitotic mechanism.

Frameshift mutations at two hotspots in vasopressin transcripts in post-mitotic neurons

Mutations in DNA underlie carcinogenesis, inherited pathology, and aging and are generally thought to be introduced during meiosis and mitosis. Here we report that in post-mitotic neurons specific frameshift mutations occur at high frequency. These mutations were identified in vasopressin transcripts in magnocellular neurons of the homozygous Brattleboro rat and predominantly consist of a GA deletion in GAGAG motifs. Immunocytochemistry provides evidence for similar events in wild-type rats. However, the diseased state of the Brattleboro rat, resulting in a permanent activation of vasopressin neurons, enhanced the mutational rate. These data reveal hitherto unrecognized somatic mutations in nondividing neurons.

Immuno-electron microscopic evidence for two different types of partial somatic repair of the mutant Brattleboro vasopressin gene

In homozygous Brattleboro rats a frame-shift mutation in the vasopressin gene prevents secretion of vasopressin by magnocellular neurosecretory neurons and thus causes diabetes insipidus. Whereas most "vasopressin" neurons in Brattleboro homozygotes apparently lack vasopressin and its associated neurophysin and glycopeptide, some isolated cells overcome the mutation and "revert" to producing readily detectable amounts of vasopressin. We describe here two morphologically and immunocytochemically distinct subsets of such "revertant" cells. One subset contain, in their rough endoplasmic reticulum cisterns, electron-dense aggregates immunoreactive for vasopressin, for parts of oxytocin-neurophysin, and for CP14 (a peptide with a sequence deduced from the mutated precursor), but not for vasopressin-associated glycopeptide ("glycopeptide") or vasopressin-neurophysin. In Brattleboro heterozygotes, which have one mutant and one normal copy of the vasopressin gene, morphologically similar revertant cells exist; the aggregates in the rough endoplasmic reticulum of these cells do not immuno-label for CP14, but the cells do produce 160-nm neurosecretory granules immunoreactive for vasopressin, vasopressin-neurophysin and glycopeptide. In Brattleboro homozygotes, the second, more abundant subset of neurons which recover vasopressin immunoreactivity also express vasopressin-associated glycopeptide and CP14 but not oxytocin-neurophysin; both glycopeptide and CP14 are restricted to the rough endoplasmic reticulum but do not form aggregates. We conclude that two different somatic repairs of the Brattleboro mutation can occur. We propose that, in aggregate-containing neurons, exons B and C have been exchanged between the vasopressin and oxytocin genes; glycopeptide-immunoreactive neurons have either undergone mismatch repair or exchanged exon B.

Dynamics of 7B2 and galanin expression in solitary magnocellular hypothalamic vasopressin neurons of the homozygous Brattleboro rat

The homozygous Brattleboro rat (di/di), displaying a hypothalamic form of diabetes insipidus, synthesizes a vasopressin (VP) precursor with an abnormal C-terminus. The phenotypic expression of coexisting peptides in mutant magnocellular VP cells shows a differential pattern. 7B2 is one of the peptides which is not detectable, whereas there is a clear galanin expression. During postnatal life a small but increasing number of solitary post-mitotic VP neurons of the di/di rat undergoes a switch to a heterozygous phenotype. Here we report the presence of 7B2 and galanin in these heterozygous cells, which suggests that for the expression of 7B2, but not for that of galanin, the relative amount of mutant VP precursor must be diminished. Possible underlying mechanisms for this differential phenotypic expression of coexisting peptides are compartmentalization of precursor synthesis within the RER or a competition for sites involved in the translocation of the functionally reduced RER.

Mutant vasopressin precursor producing cells of the homozygous Brattleboro rat as a model for co-expression of neuropeptides

The homozygous Brattleboro rat (di/di) synthesizes a VP precursor with an abnormal C terminus, which is not transported from the rough endoplasmic reticulum to the Golgi apparatus. In addition, the phenotypic expression of co-existing peptides is differentially disturbed. Ang II and 7B2 are two of the peptides which are not detectable, whereas other peptides (e.g. galanin) are clearly expressed in mutant VP cells. During postnatal life a small but increasing number of solitary post-mitotic VP neurons of the di/di rat undergoes a switch to a heterozygous phenotype. At the same time Ang II and 7B2 show up again in these heterozygous cells, which suggests that for the expression of 7B2, but not for that of other peptides (e.g. galanin), a normal VP precursor is required. A possible underlying mechanism (i.e. the existence of several domains on the endoplasmic reticulum involved in the translocation of sets of neuropeptides) for this differential phenotypic expression of co-existing peptides is discussed.

Vasopressin and angiotensin II are absent but spontaneously reappear in solitary hypothalamic neurons of the homozygous Brattleboro rat

The homozygous Brattleboro rat (di/di) synthesizes a vasopressin (VP) precursor with a different C-terminus, which is not packaged in granules. In addition, the expression of a coexisting peptide, angiotensin II (Ang II), is disturbed. During postnatal life a small but increasing number of solitary post-mitotic hypothalamic neurons of the di/di rat undergoes a switch to a genuine heterozygous phenotype. Here we report the reappearance of Ang II in these heterozygous cells, which suggests that for the expression of Ang II a normal VP precursor is required. Based upon the present study and literature data it is proposed that at the level of the endoplasmic reticulum a compartmentalization of the synthesis of various peptide precursor occurs.

Vasopressin-deficient rats show a reduced amplitude of the circadian sleep rhythm

The hypothalamic suprachiasmatic nuclei are responsible for the generation of many circadian rhythms, including the rhythm of arginine vasopressin (AVP) in the cerebrospinal fluid (CSF). We used cortical EEG recordings taken from AVP-deficient (Brattleboro strain) rats to investigate the possible role of AVP in the generation of circadian sleep/arousal rhythms. When housed either in a light-dark cycle or in constant light, Brattleboro rats showed circadian rhythms of arousal, slow-wave sleep, and paradoxical sleep. However, the amplitudes of the slow-wave and paradoxical sleep (but not arousal) rhythms in these animals were significantly lower than in controls. The results indicate that hypothalamic synthesis of AVP is not necessary for the generation of circadian sleep rhythms, but the amplitude of the rhythms may be modulated by the circadian release of AVP into CSF.

Age-related development of a heterozygous phenotype in solitary neurons of the homozygous Brattleboro rat

A single-base deletion in the single-copy vasopressin gene is the cause of diabetes insipidus in the homozygous Brattleboro rat (di/di). It results in the synthesis of an altered vasopressin precursor of which the axonal transport is blocked. Paradoxically, a small number of solitary hypothalamic neurons displays all the immunoreactivities of the wild-type vasopressin precursor (i.e., vasopressin, neurophysin, and a glycopeptide). In the present paper we provide evidence that these neurons have undergone a switch to a genuine heterozygous (di/+) phenotype; i.e., they contain the immunoreactivities of both the wild-type and the mutated vasopressin precursors. In the neural lobe, glycopeptide fibers are also present, showing that axonal transport of the wild-type precursor is restored. Moreover, the number of neurons displaying this di/+ phenotype increases markedly and in a linear way (from 0.1% up to 3% of the vasopressin cells) with age. These findings indicate that after mitotic division has ceased, genomic alterations occur in somatic neurons in vivo. The molecular event generating the di/+ phenotype in the di/di animal could involve a somatic intrachromosomal gene conversion between the homologous exons of the vasopressin and the related oxytocin genes.

The vasopressin precursor in the Brattleboro (di/di) rat

The vasopressin precursor in the rat hypothalamus has been studied, using trypsin to release desglycinamide vasopressin and coupling it to glycinamide (T & G treatment). The resulting amidated nonapeptide was detected and measured with a radioimmunoassay for vasopressin. The "vasopressin" produced in this way had the full immunoreactivity of the authentic peptide but eluted from an hplc column 1 min earlier and appeared to have a larger molecular weight. It was found that T&G treatment generated vasopressin immunoreactivity in extracts of the supraoptic nucleus (SON) of the Brattleboro rat in just the same way as it did in normal animals. Furthermore, this procedure produced vasopressin immunoreactivity in those hplc fractions from Brattleboro SON extracts that corresponded with the elution time of vasopressin precursor. Similar amounts of "vasopressin" could be generated from Brattleboro and normal SONs. These results support the suggestion that the Brattleboro SON synthesizes an aberrant vasopressin precursor which is not processed by the cell.

Cardiac baroreflex sensitivities in conscious, unrestrained, Long Evans and Brattleboro rats

Cardiac baroreflex sensitivity (BRS; i.e. the slope of the line relating change in pulse interval to change in systemic arterial pressure) was assessed in response to an increase in mean blood pressure (MBP) evoked by methoxamine or a decrease evoked by sodium nitroprusside. Measurements were made in Long Evans (i.e. control) and in Brattleboro (i.e. vasopressin (AVP)-deficient) rats, following acute and chronic intravascular catheterization, and in water-replete and water-deprived states (the latter designed to reduce plasma volume and activate AVP-dependent mechanisms (in Long Evans rats]. There were no differences between the corresponding values for cardiac BRS in Long Evans and Brattleboro rats. Furthermore, water deprivation caused no significant changes in cardiac BRS in either strain. These results do not support the claim that absence of endogenous AVP in Brattleboro rats is associated with marked impairment of cardiac BRS, and indicate that chronic changes in circulating AVP do not cause systematic changes in cardiac BRS.

Organization and efferent connections of transplanted suprachiasmatic nuclei

The hypothalamic suprachiasmatic nucleus (SCh) is the principal brain structure involved in the generation of circadian rhythms. In the present study, we have employed immunohistochemical techniques to evaluate the development of the fetal SCh following its transplantation to the brain of adult host animals. Donor hypothalami were obtained from normal Long-Evans fetuses and transplanted to the lateral, third, or fourth ventricle of Brattleboro rats. Neuronal aggregations exhibiting the organotypic features of the SCh were present in over 90% of the grafts recovered at each transplantation site. Like the normal endogenous SCh, SCh-like cell groups identified within the transplants contained a prominent population of parvicellular (9-13 micron), neurophysin-containing neurons that were immunopositive for vasopressin (VP) but not oxytocin. These SCh-like cell groups also invariably contained similar small neurons that were immunoreactive for vasoactive intestinal polypeptide (VIP). Typically, VP and VIP immunoreactive perikarya were concentrated in contiguous, complementary parts of the grafted SCh, but fibers immunoreactive for either peptide were distributed throughout the extent of the nucleus. Because the brain of the Brattleboro rat is deficient in vasopressin, it was possible to evaluate the projection of the vasopressinergic component of the transplanted SCh to the host brain. Although SCh were identified in grafts recovered from each intraventricular transplantation site, an appreciable input to the host brain could be identified only when the fetal tissue was grafted to the third ventricle. Here, grafted SCh established efferent connections with periventricular diencephalic structures which ordinarily receive a projection from the in situ SCh. Specifically, VP immunoreactive fibers originating from transplanted SCh were identified in the medial preoptic area, the periventricular and dorsomedial hypothalamic nuclei, the paraventricular nuclei of the thalamus and hypothalamus, and in the retrochiasmatic area, arcuate nucleus, and suprachiasmatic nucleus of the host brain. These results demonstrate that the fetal SCh not only survives transplantation but also retains its distinguishing cytological features and the capacity to form an appropriately restricted set of efferent connections with the brain of adult host animals.

Vasopressin cells in the medial amygdala of the rat project to the lateral septum and ventral hippocampus

The rat brain contains a large number of vasopressin (VP) immunoreactive fibers, the sites of origin of which have not yet been established completely. For instance, the sources of VP fiber systems in the amygdala, ventral hippocampus (VH), mediodorsal thalamic nucleus, ventral tegmental area, and dorsal raphe yet remain obscure. These VP fibers may originate in any of the recently described extrahypothalamic VP cell groups, viz., medial amygdaloid nucleus (AME), dorsomedial hypothalamic nucleus, or locus coeruleus, since VP efferents from these cells still remain to be demonstrated. In search of AME VP efferents three approaches were followed: (1) the Phaseolus vulgaris anterograde tracing method, (2) immunocytochemistry after AME lesioning, and (3) retrograde transport of a fluorescent dye in combination with immunofluorescence. The results demonstrate that VP cells in the AME project to (1) the lateral septum (LS) by the ventral amygdalofugal pathway and (2) the VH via the amygdalohippocampal transition zone. In addition, the VP projection from the bed nucleus of the stria terminalis (BST) to the LS was confirmed. There was no indication that VP cells in the AME project through the amygdalotegmental pathway to the medulla oblongata and spinal cord. The results support the possibility that the BST and AME are an anatomical entity that may be part of the central loci controlling sexual processes in the rat.

Vasopressin and oxytocin mRNAs in adrenalectomized and Brattleboro rats: analysis by quantitative in situ hybridization histochemistry

35S-labeled synthetic oligodeoxyribonucleotide probes were used to measure levels of vasopressin (VP) and oxytocin (OT) mRNAs in rat hypothalamus by quantitative in situ hybridization histochemistry (ISHH). VP and OT mRNA-containing cells were seen in the paraventricular (PVN) and supraoptic (SON) nuclei. VP mRNA was found to increase five-fold in the parvocellular region of the PVN after adrenalectomy while no changes occurred in magnocellular VP or OT mRNA levels. In the Brattleboro rat, VP mRNA levels were decreased and OT mRNA levels increased in the magnocellular regions. RNA species containing the VP introns were present at one fortieth of the level of processed VP mRNA in control rats. We also performed ISHH followed by immunohistochemistry on the same sections. We found that VP and its encoding mRNA were always located together as were OT-neurophysin and its encoding mRNA. In this study, we extend previous work by showing the characteristic distributions in the PVN and SON of VP and OT mRNA-containing cells and by measuring neuropeptide mRNA changes.

Propressophysin is present in neurones at multiple sites in Wistar and homozygous Brattleboro rat brain

Vasopressin (VP) is synthesized as propressophysin, containing also neurophysin (NP) and C-terminal glycopeptide (CPP), within the hypothalamo-neurohypophyseal system (HNS). Recently, VP and NP-immunoreactive cells were demonstrated in other rat brain nuclei. Here we report CPP immunoreactivity in perikarya in these nuclei. Within the homozygous Brattleboro rat, known to be deficient in neuronal VP production, no CPP immunoreactivity was seen in these nuclei. However, intense VP and CPP immunoreactivity was present in solitary cells (52.2 +/- 3.3 per rat) and fibres within the HNS.